Real-world Study of the Effectiveness and Tolerability of Outpatient Titration of OxyContin for the Moderate and Severe Pain in Cancer Patients

Primary Endpoints: The proportion of participants achieving pain remission, which is defined as the rate of participants with average NRS (Numerical rating scale) score ≤3 \[CR (Complete remission)\] or achieving a reduction of 25% when NRS score \>3 \[PR (Partial remission)\] at 72 h. Secondary Endpoints: * The proportions of participants with CR and PR at 24h and 48h * Time-to-first CR and PR * The respective proportions of participants with no rescue medication use at 24h, 48h, and 72h * Pain severity subscale score, interference of pain subscale score from the BPI-SF * The average titration dosage of OxyContin * The average maintenance dosage of OxyContin * Adverse events: the frequency and severity of adverse event